1. Field of the Invention
This invention relates to a mobile radio communication system which uses a time division multiplex.
2. Description of the Related Art
In general, a mobile radio communication system comprises a base station and first through N-th mobile stations, where N represents a positive integer which is greater than one. Each of the mobile stations may be carried by an automobile or a human being and has a variable location. The base station has a communication area in which the first through the N-th mobile stations are capable of communicating with the base station through a radio channel carrying a communication signal which may be called a time division duplex (TDD) signal.
The TDD signal has a first frame and a second frame following the first frame. The second frame may be further followed by another first frame. The first frame has first primary through N-th primary time slots which are arranged in sequential order. Similarly, the second frame period has first subsidiary through N-th subsidiary time slots.
More particularly, the first primary through the N-th primary time slots are assigned as reception time slots to the first through the N-th movable stations, respectively. The first subsidiary through the N-th subsidiary time slots are assigned as transmission time slots to the first through the N-th movable stations, respectively.
The radio channel has a channel propagation delay time which is defined by the communication area. By the channel propagation delay time, a partial overlap often occurs between the first frame and the second frame. In order to prevent the partial overlap, the second frame is followed by another first frame with a predetermined period interposed between the second frame and the first frame. The predetermined period may be determined on the basis of the channel propagation delay time.
A conventional mobile communication system may further comprise a main station connected to the base station through a communication path having a path propagation delay time. In this case, the main station communicates with the first through the N-th mobile stations by the TDD signal. The communication path may be, for example, a cable.
When the path propagation delay time is longer than a predetermined propagation delay time, interference occurs between the first frame and the second frame.